However there were a couple of things that all instructors agreed on. Firstly, all students should start with Open Games (1.e4 e5) as their first openings. And secondly, you must know the classics (as student and teacher).
I happily agree with both pieces of advice, and find the games of Joseph Blackburne suitable for use. Of course not all of games are considered classic, but they are usually straightforward and instructive. Here is one such very quick game, which can be useful in demonstrating how a big centre and an oddly placed knight on g6 can quickly turn into a winning attack for White.
Blackburne,Joseph Henry - De Vere,Cecil Valentine [C60]
BCA-02.Challenge Cup London, 1868 [Blackburne, JH]